We investigated the variation of drilled regions of expert and trainee surgeons performing virtual temporal bone surgery to identify their compliance with standard drilling procedures. To this end, we recruited seven expert and six trainee ENT surgeons, who were asked to perform the surgical preparations for cochlear implantation on a virtual temporal bone. The temporal bone was divided into six regions using a semi-automated approach. The drilled area in each region was compared between groups using a sign test. Similarity within groups was calculated as a ratio of voxels (3D points) drilled by at least 75% of surgeons and at least 25% of surgeons. We observed a significant difference between groups when performing critical tasks such as exposing the facial nerve, opening the facial recess, and finding the round window. In these regions, experts’ practice is more similar to each other than that between trainees. Consistent with models of skills development, expertise and expert-performance, the outcome of the analysis shows that experts perform similarly in critical parts of the procedure, and do indeed practice what they profess.

Do experts practice what they profess?

January
Do experts practice what they profess?
Yun Zhou 0 1
Sudanthi Wijewickrema 0 1
Ioanna Ioannou 0 1
James Bailey 1
Gregor Kennedy 1
Debra Nestel 1
Stephen O'Leary 0 1
0 Department of Surgery (Otolaryngology), University of Melbourne , Melbourne , Australia , 2 Department of Computing and Information Systems, University of Melbourne , Melbourne , Australia , 3 Melbourne Centre for the Study of Higher Education, University of Melbourne , Melbourne , Australia , 4 Department of Surgery (Austin), University of Melbourne , Melbourne , Australia
1 Editor: Andrew R. Dalby, University of Westminster , UNITED KINGDOM
We investigated the variation of drilled regions of expert and trainee surgeons performing virtual temporal bone surgery to identify their compliance with standard drilling procedures. To this end, we recruited seven expert and six trainee ENT surgeons, who were asked to perform the surgical preparations for cochlear implantation on a virtual temporal bone. The temporal bone was divided into six regions using a semi-automated approach. The drilled area in each region was compared between groups using a sign test. Similarity within groups was calculated as a ratio of voxels (3D points) drilled by at least 75% of surgeons and at least 25% of surgeons. We observed a significant difference between groups when performing critical tasks such as exposing the facial nerve, opening the facial recess, and finding the round window. In these regions, experts' practice is more similar to each other than that between trainees. Consistent with models of skills development, expertise and expert-performance, the outcome of the analysis shows that experts perform similarly in critical parts of the procedure, and do indeed practice what they profess.
-
Data Availability Statement: All relevant data are
within the paper and its Supporting Information
file.
Funding: The authors received no specific funding
for this work.
Competing interests: The authors have declared
that no competing interests exist.
Introduction
The traditional apprenticeship model, where trainees practice and refine their surgical skills
under the supervision of expert surgeons is regarded as the gold standard in ENT training [
1,
2
]. A shortage of cadavers, limited availability of experts, limitations in working hours of
trainees, and lack of objective assessment methods has led to the development of new training
methods such as Virtual Reality (VR) simulation. Surgical simulators typically provide the user
with a 3D representation of the operative field, within which surgical tools are used to perform
procedures on a ªvirtual patientº. Simulations may also render force-feedback and/or sound to
improve the fidelity of the virtual operative experience. One of the advantages of using VR in
surgical training is the opportunity to record performance metrics directly from the simulator,
and from these, derive objective assessments of operative skill.
In our previous work, we have shown that expertise can be determined from
simulator-generated metrics that relate to surgical technique [
3, 4
]. Here, we seek to test a dogma at the heart
of surgical practiceÐthat at critical stages of an operative procedure experienced surgeons will
not deviate from a ªstandardizedº technique. It may seem self-evident that this would be the
case, but observation of expert surgeons in routine surgery show that they deviate from the
didactic approach to the surgery that they teach. This in fact appears to be a reproducible
characteristic of the expert; as a learner moves from foundational study through basic competence
to true expertise, there is a move away from a protocol-driven technique to a flexible approach
to a problem [
5, 6
]. This has been viewed as the essence of expertise [
6, 7
], and is thought to
reflect an expert drawing upon a wealth of experience that can be adapted to each new
situation. These observations are often in contrast to the way in which experts present their own
approach to complex surgeryÐleaders in the field publish and present detailed protocols on
how to deal with critical aspects of an operation. This begs the question as to whether experts
actually do as they profess when dealing with the most crucial aspects of an operation. VR
simulation provides a new way to test this, through the analysis of simulator-generated metrics.
The operative procedure evaluated in this paper is temporal bone surgery. The temporal
bone houses the outer, middle and inner ears. It is dissected during operations to treat chronic
otitis media, implant auditory prosthesis, treat diseases of the facial nerve or access the skull
base [
8, 9
]. During these procedures, a surgical drill is used to remove the bone surrounding
critical anatomical structures that are embedded within it, such as the facial nerve or the main
venous sinuses draining the head. To investigate if and when expert surgeons develop their
own ªstylesº of drilling in temporal bone surgery, we examine the variability of drilled areas in
different regions of the temporal bone and relate this data to the perceived criticality of the
corresponding phase of the surgery. We postulate that there will be less variability when accepted
surgical opinion dictates that most caution needs to be exercised. The use of simulation in this
way opens up for the first time an experimental method to study this question of whether
experts do indeed follow standard guidelines they advocate when training mentees. These
investigations could lead to a better understanding of how an expert surgeon behaves when
there is perceived risk, enable better conceptualization of expertise, and in addition assist in
the development of automated performance evaluation techniques.
Materials and methods
Simulation platform
The surgical outcomes analyzed in this study were recorded on the University of Melbourne
VR temporal bone surgery simulator [
10
]. In this simulator, major anatomical structures that
need to be identified without injury during surgery, such as the sigmoid sinus, dura, facial
nerve, chorda tympani, and round window membrane are represented in a 3D model of the
temporal bone. Surgeons interact with the virtual temporal bone using a haptic device to drill
the virtual temporal bone (see Fig 1).
Experimental design
Participants undertook a specific operation of the temporal bone, involving the surgical
preparation for cochlear implantation. In this operation, the bone of the mastoid is removed
(ªcortical mastoidectomyº), and then the bone between the facial nerve and the nerve for taste (the
chorda tympani) is drilled away in order to enter the middle ear (to create a ªposterior
tympanotomyº). Finally, the surgeon enters the cochlea with a fine diamond burr (i.e. performs a
ªcochleostomyº). The cochleostomy provides the cochlear implant electrode access to the
inner ear and is performed using the cochlea's round window as a landmark to ensure that
structures of the inner ear are not damaged. For this reason, the round window is exposed
prior to undertaking the cochleostomy. In this operation, the critical steps are the performance
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Fig 1. A surgeon performing temporal bone surgery on the University of Melbourne temporal bone surgery simulator. The image is presented on a 3D
screen, with the user wearing 3D goggles. A haptic enabled 3D pointing device (right hand) is used to interact with the virtual model, and represented in the
simulation as a drill (as shown on the screen). Simulation parameters are adjusted with a MIDI interface controller (left hand).
of the posterior tympanotomy when the facial nerve and chorda tympani are at risk of injury,
identification of the round window as this provides the surgical landmark for siting the
cochleostomy, and then the actual placement of the cochleostomy.
Our hypothesis is that when experts perform this operation that there will be much less
variation in the removal of bone during these critical steps of the operation than at earlier stages
in the procedure. The hypothesis was tested by comparing the variance in bone removal for
experts with that of surgeons who have had considerably less experience (trainee surgeons in
Otolaryngology Head and Neck Surgery). Variance in bone removal was assessed for each of
the steps of the procedure. We predicted that when the critical stages of the operation were
reached (posterior tympanotomy, exposure of the round window, and cochleostomy) that
there would be significantly less variance in the bone removed by the experienced surgeons
than by the trainees. Conversely, for the less critical steps there would be less difference
between these groups.
Participants
Seven consultant and six trainee ENT surgeons performed the entire preparation procedure of
the temporal bone for cochlear implantation on the University of Melbourne VR temporal
bone surgery simulator. Ethics approval for this study was granted by the Human Research
Ethics Committee of the Royal Victorian Eye and Ear Hospital, East Melbourne, Australia
(Approval ID: 12/1075H). Written informed consent was obtained from all participants.
3 / 12
Derivation of surgical regions
For the analysis of bone removal, the specimen was divided into different anatomical regions.
Anatomical structures are used as landmarks by surgeons during a procedure, and as such,
this spatial division is a natural way of segmenting a surgical procedure into steps. Further,
areas associated with anatomical structures are inherently related to the technique and location
of bone removal with the surgical drill.
The virtual specimen in the simulator is represented in the volumetric 3D grid, where a
voxel represents a grid cell in 3D space. Each voxel contains an attribute to indicate whether it
belongs to an anatomical structure segment or the temporal bone. To divide the specimen into
regions, standard morphology operations in image processing (dilation and erosion) were
performed on the voxels belonging to anatomical structures [
11
].
To obtain the regions around structures such as the dura, sigmoid sinus, facial nerve, and
round window, the structure boundaries were expanded in each direction in 3D space, using a
dilation operation. To obtain areas between structures such as the facial recess, a dilation
operation was followed by an erosion (shrinking of the structure boundaries), which is a commonly
used operation for filling holes. The width of the area around an anatomical structure to be
considered as a region was chosen per structure manually by an expert. The area between the
dura and the sigmoid sinus which was not part of the computed drill regions was considered
to be the center region where surgeons would make their initial cut into the mastoid bone. The
region divisions of a temporal bone specimen are illustrated in Fig 2.
Determination of variation
To determine drilling variations between expert and trainee ENT surgeons, the number of
participants in each group that drilled each voxel in each region was calculated. This measure was
normalized to obtain the percentage of participants who drilled each voxel to compensate for
unbalanced participant numbers. This percentage value for each voxel in the expert and novice
groups was compared using a sign test. The voxels no surgeon drilled were ignored.
To determine the variation within each group, a similarity measure was defined as aa7255%%,
where αm refers to the number of voxels drilled by at least m% of participants in the group.
The thresholds of 25% and 75% were chosen as they are conventional numbers used in
descriptive statistics to divide data sets into groups. This measure has two advantages. First, it
removes voxels drilled by a low number of surgeons, thus removing any outliers in the data.
Second, by considering voxels drilled by a majority of surgeons, but not necessarily all of them,
it accounts for small variations that naturally occur when performing a surgical procedure. A
high value in the similarity measure represents high coherence in the areas drilled by surgeons
within a group in each region.
Data analysis
Results
The non-parametric sign test was used in the comparison of groups to avoid assumptions of
normality. A confidence interval of 95% was considered when testing for significance
(p 0.05). Data analysis was performed using Matlab R2015a.
Results of the sign tests indicated that the expert and novice groups showed significant
differences when drilling in the regions of facial nerve (p<0.001), facial recess (p<0.001), and round
window membrane (p<0.001). In these areas, the similarity of the drilled areas, within the
expert group was higher (see Fig 3).
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Fig 2. Region divisions in the temporal bone. (a) center region, (b) region around the dura, (c) region around the sigmoid sinus, (d) region near
the facial nerve, (e) posterior tympanotomy (facial recess), and (f) region around the round window.
Heat maps in Figs 4±9 illustrate the differences in drilled areas of the two groups in each
region. At each voxel, the colour variation indicates the percentage of surgeons that drilled
that voxel. The colour changes from dark blue through light blue, yellow, orange, and red to
dark red indicating a gradual increase in percentage from lowest to highest.
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Fig 3. Similarity of drilled areas in different regions of two groups. Similarity is defined as the ratio of the number of voxels in a region drilled by at least 75% of
the surgeons in a group and that drilled by at least 25% of the surgeons.
Discussion
We have found that experts exhibited greater concordance in the bone drilled during the
critical stages of the procedure (skeletonising the facial nerve, drilling in the facial recess, and
exposing the round window), than the less-critical cortical mastoidectomy stage (central
region and areas around the dura and sigmoid sinus). There was no significant difference in
the consistency of bone drilled by experts and residents in the cortical region, while experts
had significantly greater consistency than residents in the critical stages of the procedure.
Fig 4. Heat map of drilled voxels in the central area for: (a) expert and (b) trainee groups. No significant difference was observed
between groups.
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Fig 5. Heat map of drilled voxels around the dura for: (a) expert and (b) trainee groups. No significant difference was observed between groups.
These findings support the hypothesis that experts adopt a consistent approach at critical
stages during an operation, but at other times are more flexible.
The heat maps for the regions of the facial nerve (Fig 7), facial recess (Fig 8), and round
window (Fig 9) show the bone drilled during the critical parts of the operation. Almost all
experts opened up the facial recess wide enough for the round window to be viewed
completely. On the other hand, most of the trainees did not drill enough of the posterior
Fig 6. Heat map of drilled voxels around the sigmoid sinus for: (a) expert and (b) trainee groups. No significant
difference was observed between groups.
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Fig 7. Heat map of drilled voxels near the facial nerve for: (a) expert and (b) trainee groups. Significant differences
were observed between groups. Experts were more similar in their drilling in this region than the trainees.
Fig 8. Heat map of drilled voxel in the facial recess for: (a) expert and (b) trainee groups. A significant difference was observed between groups. The
expert group was more similar in how they drilled in this region compared to the trainees.
tympanotomy and thereby encountered difficulties when exposing the round window.
Visualisation of the round window was achieved by experts exposing the facial nerve and chorda
tympani thoroughly, and more completely than trainees. In accordance with expert advice on
performing a cochleostomy [12], visualization of the round window is required in order for
surgeons to have sufficiently good landmarks to choose the correct location of cochleostomy.
We find that experts do this in a consistent manner with little variation, both through their
preparation of the posterior tympanotomy and also the attention given to removing the bone
overlying the round window.
Fig 9. Heat map of drilled voxel around the round window membrane for: (a) expert and (b) trainee groups. A
significant difference was observed between groups. The expert group was more similar in how they drilled in this
region compared to the trainees.
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While the surgery of trainee surgeons varied much more than that of experts during the
critical stages of the surgery, their drilling behavior was quite similar to that of experienced
surgeons during earlier stages of the surgery. The cortical mastoidectomy in this particular
operation is simply an approach to find the facial nerve and perform the posterior
tympanotomy, which means that full exposure of all of the anatomical structures encountered was not
necessary. It appears from these results that surgical residents have the knowledge and
technical skill to perform the cortical mastoidectomy adequately. There could be several explanations
for the lack of consistency during the critical phases of the operation. It may be tarinee
surgeons did not have the knowledge to appreciate the need for a consistent approach, or it may
be that they lacked the surgical skill to execute one. Differentiation between these factors may
prove to be difficult. Trainees knew where to find the facial nerve and chorda tympani, but did
not remove bone overlying these nerves adequately. These trainees were likely apprehensive,
as they would have been aware that permanent impairment results from injuring the nerves.
In addition, considerable technical skill is required in order to skeletonize them. Finally,
trainees need to appreciate that skeletonization is necessary in order to visualize the round window.
The extent to which the relative inexperience of a trainee surgeon manifests in fear, more
limited technical ability or less extensive knowledge is difficult to ascertain.
These observations are consistent with the broad literature on models of skills development
[13], expertise [
14, 15
] and the expert-performance approach [16]. Eraut [
7, 17
] states that
experts no longer rely on rules or guidelines; have an intuitive grasp of situations based on a
deep tacit understanding; employ analytic approaches used only in novel situations or where
problems occur; and have a vision of what is possible. According to Dreyfus et al. [
14, 18
], the
expert, having progressed through novice, competence and proficiency stages has high levels
of procedural knowledge and skills (knowing how) as well as declarative knowledge (knowing
what), and contextual flexibility (knowing when and where). Dunphy and Williamson [
5
] note
that expert performance does not rely on principles or rules to connect understanding of the
situation to an appropriate action.
The variations observed in the non-critical aspects of the procedure show that the experts
in our study were comfortable in their practice to take shortcuts and develop their own style of
surgery because they possessed the intuition and tacit knowledge to do so safely. Indeed,
knowing when to follow rules, and when not to, in itself is an aspect of expertise embodied in
the characteristics of ªpattern recognitionº±the ability to identify complex patterns, and
ªflexibilityº±the ability to approach each situation with a high level of flexibility [
5
]. Moulton et al.
describe this approach as ªslowing down when you shouldº to stay out of trouble during
surgical practice [
19
]. It is not necessarily a slowing down temporally but a shift from automaticity
to effortful modes. Indeed a subset of surgeons involved in their qualitative studies
ªvehemently objected to ever being in the automatic modeº. Others acknowledged the state of
ªdriftingº describing approaches to routine practice in which they may not have engaged in the
continuous essential monitoring of their progress. What is important here is that effortful
modes require cognitive space to deal with the changing conditions of the procedure. From
this perspective, the experts in our study are likely to have adopted this effortful mode as they
approached the critical points of the procedure.
The strength of this study is that it enables us to directly compare expert and trainee
surgeons' performance of critical and other aspects of surgical preparation, with cochlear
implantation on a virtual temporal bone as the ªtest caseº. This study offers insight to the level of
skills development±product-oriented (the end result) rather than process-oriented (how things
are done). Given the significant differences between trainees and experts, this VR environment
offers tremendous research opportunities to focus attention on the process-orientation to gain
deeper understanding of how the expert is achieving superior performance. This is a reflection
9 / 12
of the type of information that can be gleaned with such a systemÐa continuous stream of
data on how a surgeon handles instruments and interacts with the anatomy that they
encounter. However, this strength also carries a limitation; the skills are performed out of context and
therefore may not reflect the environmental and sociocultural pressures of real clinical
environments (i.e. the operating theatre) in which trainee and expert surgeons are expected to
perform [
20, 21
]. In some ways then, these results are even more striking since trainees are likely
to be under greater pressure than experts in real work settings. It is also important to keep in
mind that the models of skills development and expertise we have outlined focus on
individuals and that safe surgical operating extends beyond the expertise of one individual.
The critical points in this surgical simulation may be better represented by a different
theoretical approach. Threshold concepts are described as being ªakin to a portal, opening up a new
and previously inaccessible way of thinking about something. They represent a transformed
way of understanding, interpreting, or viewing something without which the learner cannot
progressº [
22
]. Threshold concepts are further characterized as irreversible, in that once
acquired the change in perspective or behavior which has been produced by the threshold
concept is unlikely to be unlearned, it may even be difficult to comprehend the state of those on
the other side of the threshold who are unable to comprehend the meaning of what is
happening because they do not understand it [
22
]. Threshold concepts are transformative in that they
lead to a change in perception and in certain powerful instances, this change may have an
associated shift in identity. We posit that the critical points in this simulated surgical environment
represent a threshold concept. Trainee surgeons are in a liminal state where they may recognize
the critical points but are not yet able to successfully progress to the expert state because they
have not undergone the required ontological shift associated with being an expert surgeon.
Although mimicry of superior performance will likely add value in VR, true expertise demands
the ability to deal with contextual complexity currently not represented in our simulation.
These results provide valuable insights into expert behavior. Surgeons do act similarly when
the stakes are high in an operationÐthey revert to standardized procedure, even though
exhibiting flexibility at other times. In other words, it appears that experienced surgeons adopt the
view that surgical error is least well tolerated when the consequence or a mistake is greatest,
and that the best way to mitigate this risk is to adopt a standard approach at these critical
moments during surgery, what Moulton et al describe as moving to an ªeffortful modeº. This
is akin to the ªstandard operating proceduresº (SOP) adopted in aviation or other contexts
when risk is high and failure catastrophic. This supports the practice of surgeons ªfollowingº
the leadership of esteemed colleagues, and emphasizes the value of following prescriptive
descriptions of complex surgical cases.
Supporting information
S1 File. This file contains the data and Matlab code used in the discussed study. Extract the
zip file and run the file `main.m'. The folder `Data' holds the anonymized expert and trainee
data.
(ZIP)
Author Contributions
Conceptualization: Yun Zhou, Ioanna Ioannou, James Bailey, Gregor Kennedy.
Data curation: Yun Zhou.
Formal analysis: Yun Zhou, Sudanthi Wijewickrema, Ioanna Ioannou, Gregor Kennedy.
10 / 12
Investigation: Yun Zhou, Sudanthi Wijewickrema, Ioanna Ioannou.
Methodology: Yun Zhou, Sudanthi Wijewickrema, Ioanna Ioannou, James Bailey.
Software: Yun Zhou.
Validation: Sudanthi Wijewickrema, Debra Nestel, Stephen O'Leary.
Writing ± original draft: Yun Zhou.
Writing ± review & editing: Sudanthi Wijewickrema, Ioanna Ioannou, James Bailey, Debra
Nestel, Stephen O'Leary.
11 / 12
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